This invention relates to an apparatus for building pneumatic tires and more particularly to such apparatus which includes a pair of flanges suitable for positioning a partially built first stage "green" or uncured tire for shaping by the apparatus.
A tire building apparatus as described, for example, in U.S. Pat. No. 3,923,572, comprises a center shaft and an elongated sleeve on the center shaft, a pair of axial movable bead carrier flanges situated diametrically about a transverse plane which is normal to the center shaft and a screw means which positively drives or moves each flange axially about the transverse plane. Each flange includes a bead seat. One flange contains an inflation port for access to the interior of an air chamber formed when a tire carcass is mounted on the flanges.
When building a tire on such a tire building apparatus, the flanges are axially set about midway toward the transverse plane. The first stage green tire consisting of a carcass, a pair of bead portions, and a pair of sidewalls is placed on the apparatus such that each bead portion is positioned in a corresponding bead seat on each flange. Thereafter, the flanges are actuated to move each flange axially outwardly from the transverse plane to lock and support each bead portion in the corresponding bead seat. As each flange moves axially outwardly, the surface of each bead portion of the tire slides on the surface of the bead seat allowing proper positioning of the bead portion in the bead seat.
When the bead portions are suitably supported in corresponding bead seats, the axial outward movement of each flange is stopped. The air chamber is filled with air to inflate the first stage green tire during which the flanges are actuated to move axially inwardly towards the transverse plane allowing for shaping of the tire carcass to substantially its final diameter. When the first stage green tire is suitably shaped, an inextensible belt assembly and tread can be applied to the first stage green tire thereby forming a completely built second stage green tire.
After completion of building the green tire (e.g., by placing the belt assembly and tread around the expanded carcass), the air chamber is deflated, the bead portions are separated from the bead seats, the flanges are moved axially inwardly and the second stage green tire is removed from the tire building apparatus.
It has been found when mounting each bead portion on the corresponding flange, the bead portion does not easily slide on the surface leading to the bead seat and each bead portion generally adheres or sticks to the bead seat wherein the bead portion and the bead seat do not separate when the flanges are moved axially inwardly.
It is believed that the reason for such sliding difficulty is due to the interaction between the surface of the bead seat and the outer surface of each bead portion which includes a rubber coated finishing strip. Generally, such finishing strips are made of woven fabric which is coated on both sides with uncured rubber which is tacky and will stick to the bead seat when the green tire is being positioned on the flange. Furthermore, it is believed that the contact of the bead portion to the bead seat forms a pneumatic seal which prevents the release of the bead portion from the bead seat upon completion of the green tire.
Attempts to overcome the sliding difficulty and adhesion of the outer surface of the bead portion and the bead seat of the flange include periodical cleaning of the bead seat area with a lubricant such as castor oil. However, it has been found that such lubricants can be transferred to other areas of the tire wherein the lubricant is a contaminant. Also, application of such lubricants has resulted in a problem of buildup of polymerized castor oil in the bead registers of tire molds found in curing presses, resulting in additional maintenance.